5 Things to Watch in South Carolina's Republican Primary

COLUMBIA, S.C. -- Iowa and New Hampshire did their jobs. While we started the campaign cycle with 17 Republican presidential candidates, the specter of the nation's first two voting states has culled the field to six.

For the last 30 years, though, South Carolina voters have had a different role: to choose the nominee.

As the polls open Saturday, here are the storylines we're following in the First in the South primary.

1. Another Trump Runaway?While polls tightened and eventually gave way to a loss in Iowa, Donald Trump played his hand to perfection in New Hampshire: a 20-point victory over a crowded field across a variety of voter groups.

Trump may see a similar scenario play out in South Carolina, despite completely different demographics: in a state where large proportions of evangelicals were supposed to favor Texas Sen. Ted Cruz, several polls show the Manhattan millionaire beating the son of a Baptist preacher by double digits.

Trump also commands large swaths of loyal veterans -- a big plus in a state that's home to active bases for each military branch.

If Trump wipes the floor with Cruz in the Palmetto State, the question has to be asked: will he do the same across the South on March 1st in the vaunted "SEC Primary?"

2. The Nastiness FactorThe "aw, shucks" days of Iowa and New Hampshire are over: South Carolinians have a distressfully high tolerance for negative campaigning.

Late this week, residents told ABC News they were receiving more than a dozen "robo-calls" a night. A recent one, released Thursday night by the pro-Cruz Super PAC Courageous Conservative Political Action Committee, bashed Trump for encouraging the removal of the Confederate flag from the South Carolina state house.

"People like Donald Trump are always butting their noses into other people's business," a grave voice intones. "Trump talks about our flag like it's a social disease."

Negative advertisements are one thing. Genuine deception is another. Marco Rubio supporters called foul this week over an apparent Facebook post from supporter and South Carolina congressman Trey Gowdy, who abandoned the Florida senator and endorsed Cruz instead.

The post was actually from a different account that resembled Gowdy's name -- a trick that's par for the course in what has become one of the most contentious cycles in recent memory.

Rubio campaign sends out email warning voters of "primary day tricks by Cruz"

- Ines de La Cuetara (@InesdLC) February 19, 2016Elections officials will also be kept on their toes looking for any false information or irregularities regarding polling places. Democrats won't vote for another week, which could sow seeds of confusion among low-information voters.

3. Bush's Last Stand?On Friday night, at his last event before polls opened in South Carolina, Jeb Bush's words hung in the air.

"I want to thank you for allowing us to close out our campaign here," he told the crowd. "God bless you."

"I want to thank you for allowing us to close out our campaign here." -an ominous closing from @JebBush here in Central, SC.

- Candace Smith (@CandaceSmith_) February 20, 2016Ostensibly, the former Florida governor was talking about the end of his campaign in South Carolina. But could the awkward phrasing have been a sign of larger things to come?

Those around him have long viewed the Palmetto State as Bush's firewall -- a Southern state with extensive family ties. His father George H.W. Bush won the state twice, as did his brother, George W. Bush. The 43rd President stumped for Jeb this week, along with his mother, Barbara, and South Carolina Sen. Lindsey Graham.

"South Carolina is Bush country," Graham declared.

The votes haven't seemed to materialize. Bush has lagged far behind Trump and Cruz in nearly every statewide poll, and appears to be angling for third. A drubbing by Rubio, or even a narrow loss to Ohio Gov. John Kasich, could spell the end of his run.

4. Record Turnout ExpectedThe last presidential election brought an all-time high in turnout for the GOP, with 603,770 South Carolinians casting ballots in a contested primary. But this year is widely expected to break that mark.

In fact, records are already falling -- while a record 35,595 absentee ballots were cast in the 2012 Republican primary, more than 38,000 GOP ballots had already been cast as of midday Thursday, and more poured in through the end of the week.

As the conventional thinking goes, the large numbers favor Trump, who by all accounts has brought new voters into the fold. But Iowa's swollen numbers resulted in a win for Cruz -- a testament to a sophisticated ground game that also swiped a better-than-expected third place finish in New Hampshire.

This is what you see wandering downtown Columbia 2 days before the #SCPrimary. @tedcruz vols working the phones. pic.twitter.com/h1ZB9P9QQI

- Brad Mielke (@TheBradMielke) February 19, 20165. Watch out for Lexington CountyThe county that sits smack dab in the center of South Carolina is also considered its bellwether.

Despite wildly different outcomes from 2008, when John McCain narrowly beat Mike Huckabee, and 2012, when Newt Gingrich trounced Mitt Romney, Lexington County predicted the winner both times.

South Carolina analysts will have an eye on it.

While Lexington is a bellwether for the state, the state may well be a bellwether for the nation. South Carolina is known for being more representative of the American electorate than New Hampshire or Iowa. Its population is nearly quadruple that of New Hampshire, making it a better indicator of larger states to come on the election calendar.

It's also racially and ideologically diverse. Its Republican voters count more moderates than those of the two early-voting states. Its choice will go far in selecting the next nominee, as it does every four years.

Welcome to the South Carolina primary.

ABC News' Alana Abramson and Ryan Struyk contributed reporting.